Employing light emitting diode (LED) in high power illumination, besides continuously promoting brightness, heat dissipation is another main problem that is indeed necessary to be solved. When light extraction efficiency is not good, the light, which cannot pierce a light-emitting device including LED and its encapsulant, transforms into heat. If the heat cannot be dissipated out of the light-emitting device effectively, the temperature is going to raise during operation. Thus, reliability problem comes out. Prior arts provide a lot of methods for solving the problem of heat dissipation of elements. Taking a light-emitting element having GaN series grown on a sapphire substrate as example, double transfer method is used to remove the sapphire substrate with worse heat dissipation by laser lift-off or chemical etching, then a silicone substrate with better heat dissipation is connected to the light-emitting element in order to improve the heat dissipation effect of the light-emitting element. Another improving method is to take flip-chip bonding to replace traditional wire bonding. FIG. 1 shows that a known light-emitting device with flip-chip bonding comprises a LED 10 and a submount unit 20. Solder bumps 24 are formed on a first bond pad 22 and a second bond pad 23, for connecting the LED 10 to the submount unit 20 in a bonding process. The solder bumps 24 are formed on the first bond pad 22 and second bond pad 23 one by one through the gold stud bump method. Through thermosonic bonding method, ultrasonic wave is provided on the junction of the solder bumps 24 of the submount unit 20 and electrodes 15 and 16 of the LED 10 to make the junction quickly rub to produce high heat for melting and bonding. Generally, diameter of a gold stud is about 50 um. Dimension of every gold stud must be close to avoid that the short gold stud cannot tough the junction to influence the characteristics of products and bonding performance. In addition, because the gold stud is that the front of a gold wire is melted to become a spheroid and then is bonded on the submount through thermosonice bonding, dimension of the gold stud is restricted to that of the gold wire not to be further contracted. Thickness is still larger than 20 um after bonding so the thermal resistance between the LED 10 and a submount 21 cannot be reduced. Thus, the application of the LED 10 in the high power device is restricted.
Therefore, this invention provides a light-emitting element which is applicable to direct flip-chip bonding, without additional solder bump on the submount. This invention also comprises the advantages of wide bonding area, short bonding distance, high heat dissipation, great reliability, and low cost.